Preparation

Preheat oven to 375 degrees F.

Put the butter in a small saucepan and set over medium-high heat. Heat, swirling the pan occasionally until the butter melts halfway. Remove from heat and swirl the pan occasionally until the butter melts completely.

While the butter is melting, use a fork to whisk together the all-purpose flour, buckwheat flour, almond flour, sugar, and salt.

Once the butter is melted, add it to the flour and stir with a fork until mixed together. Transfer to a 9-inch round tart pan and use your fingers to press the dough evenly and firmly into the bottom and up the sides of the pan. Set on a baking sheet and bake for 20 minutes.

While the crust bakes, mix together the ingredients for the wild blueberry filling.
After 20 minutes, remove the tart crust. Use a metal measuring cup or glass jar to press the bottom and sides of the crust firmly against the pan, so it hugs the tart pan nicely. Pour the wild blueberry filling into the pan. Bake on the baking sheet until nicely browned, another 20 to 22 minutes.